1. Field of Invention
The present invention relates to a method for making a conductive polymer composite and, more particularly, to a method for making a conductive polymer composite for detecting a sort of gas.
2. Related Prior Art
Referring to FIG. 1, a sensor for detecting a sort of gas was disclosed by Keat Ghee Ong, IEEE Sensors Journal, vol. 2, No. 2, April 2002. The sensor includes a substrate 10, electrodes 11 provided on the substrate 10, an insulating layer 12 provided on the substrate 10, and a conductive composite film 13 provided on the insulating layer 12. To make the conductive composite film 13, multi-walled carbon nanotubes 131 are evenly mixed with silicon dioxide solution, and the mixture is coated on the insulating layer 12 and dried so that water is removed from the mixture. Thus, the conductive composite film 13 includes multiple conductive paths. Some of the multi-walled carbon nanotubes 131 stick out from the silicon dioxide base 132. Thus, the multi-walled carbon nanotubes 131 that stick out of the silicon dioxide base 132 attract a sort of gas so that the dielectric constant and conductivity of the multi-walled carbon nanotubes 131 are changed and that the concentration of the sort of gas is detected.
Another sensor for detecting a sort of gas was disclosed by Jose K. Abraham, Smart Material Structure, 13, (2004) 1045-1049. The sensor includes a circuit board, electrodes provided on the circuit board, and a conductive composite coating provided on the circuit board. To make the conductive composite coating, carbon nanotubes are mixed with gas responsive polymer such as polymethylmethacrylate (“PMMA”) are evenly mixed with each other in a solvent by ultrasonic waves, and the mixture is coated on the circuit board and dried to remove the solvent from the mixture. Thus, on the circuit board, there is formed a conductive composite coating similar to the conductive composite film shown in FIG. 1. The polymer attracts a sort of gas so that it expands and changes the conductive paths of the carbon nanotubes on the polymer base and the resistance so that the concentration of the sort of gas is detected. Some of the carbon nanotubes that stick out of the polymer however also attract the sort of gas and change the conductive paths thereof. Thus, the detection of concentration of the sort of gas is complicated, the reproducibility is poor, and errors could easily occur.
A sensor array has been disclosed in U.S. Pat. No. 6,759,010. The sensor array includes various sensors for detecting the concentrations of different substances. The disclosure of U.S. Pat. No. 6,759,010 is incorporated in the present application.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.